Base shield and method



March 14, 1950 c, SCHELL 2,500,384

BASE SHIELD AND METHOD Filed July 18, 1946 I I I BY ar es c e uiz/$46M His fll'i'or-ney Patented Mar. 14, 1950 UNIT AT'ENT OFFICE BASE SHIELD AND METHOD of Massachusetts Application July 18, 1946, Serial No. 684,608

3 Claims. I

The-present invention relates to electron tubes and to the basing of radio tubes and the like, and more particularly to the structural formation of a cylindrical metal sleeve located at the base of electron tubes, and to an improved method of forming the shield.

In tubes using a metal sleeve as a shield of the character described, the electrodes are housed within an evacuated or a gas filled glass envelope closed at one end by a header through and to which the several axially extending lead-in wires are hermetically sealed. This header end of the envelope is seated against relative rotary movement upon a wafer-like base of Bakelite or similar hard dielectric material having a plurality of axially extending tubular terminal pins within which the lead-in wires are threaded and soldered to place.

Shields of this character'heretoforehave comprised tubular members first drawn cup-shape from a flat stock and then made into a seamless tube by having their bottom walls punched out. This punch press method while producing a desirable shield has been costly and it is the principal object of my invention to provide an improved construction which may be fabricated much faster and far more economically.

Another object of my invention is to provide an improved construction so that even though slight variations may occur in the blank from which the shield is made a satisfactory shielded tube still results.

In the arrangements illustrated in the drawing, I provide a tubular member formed from strip metal to be used as a shield in the basing of radio tubes and the like, with a straight wall rolled long its top edge to form an inwardly turned annular flange, and having a lock seam extending but part way of its width, the opposing ends of the strip above and below the seam in abutment, the seam being pressed inwardly, all of which provides a smooth joint which throughout its entire length lies flush with the outer cylindrical surface.

The accompanying drawings illustrating the invention and forming a part of the specification axially from the base I.

Fig. 5 isan enlargedtop plan view of the shield.

Fig. 6 isa sectionalview on line 6-43 of Fig. 5.

AndFig. 7 is a view, drawn to a reduced scale, showing a length of strip material and the operations performed thereon prior to its reaching horizontal sliding dies which in cooperation with a common mandrel givesit cylindrical shape and form the seam.

In the drawings similar reference numerals refer to similar parts throughout the several views.

The base with which the shield is used is a disc-like wafer i of Bakeliteor other hard dielectric material upon which is seated the header end 2 of the glass envelope 3. Electrodes within the latter are not shown as the interior construction and arrangement of the tube have no particular bearing on the invention. Lead-in wires, also not shown, are hermetically sealed in the header 2 and extend through bosses i on the bottom thereof, the projecting ends of the wires being threaded into and soldered to respective ones of regularly spaced, circularly arranged tubular terminal pins 5 secured to and extending In the top of the base are pockets 6 adapted to receive the bosses 4 and its peripheral edge is reduced to provide a supporting ledge l for the cylindrical shield 8 and an annular shoulder 9 over Which the shield engages and which is locating means for centering themember-B andholding it in concentric spaced relation to the envelope. Thiscomparatively narrow spacing is preferably closed at its upper end by rounding the to edge of the shield into a flange I'll. Before assembly a ring H of basing cement ismechanically applied to the inner face of the shield 8 and after assembly of the parts is hardened by a localized external application of heat to the shield, thus effectively sealing the latter to the envelope 3.

The peripheral edge of the base I has a plurality of regularly spaced radial notches I2 each being of .a depth suificient to form an undercut surface l3. At these points the shield is staked by a suitable kick press which forces registering portions 54 of the shield along its bottom edges inwardly to lockingly engage the surfaces 13 and thus hold the shield against axial displacement.

I shall now describe a method for fabricating my improved shield construction:

The shields 8 are made such as on a four-way slide machine from strip -metal l5 fed from a roll along suitable guides. The feed is intermittent but at high speed and at a first station A a cutting tool operates to form opposing, open ended rectangular notches l6 while simultaneously a second operation takesplace at station B, a third operation on the top edge of the strip between stations B and C, and a fourth operation at station D.

At station B a pressure pad engaging the face of the strip produces a slight embossing ll between opposing slots I6 which is of a greater width than that of the slots, and cutting dies function to slit the body of the strip in line with the bottoms of the slots to approximately the side edge of the embossing. That portion of a strip comprising the cylindrical wall of a shield is indicated by dimension Y, Fig. 7, the top edge of this portion of each blank when between stations B and C being engaged by a suitable tool to form the flange 10.

At station D the strip is cut transversely along a line intermediate the side edges of opposing slots I6, thus severing a blank such as illustrated at l, Fig. 4, and forming the longitudinally projecting end 18 of one blank and a like part IE, but of different length, of the succeeding blank.

From station D, the strip is fed to a mandrel, not shown, in cooperation with which four angularly arranged slides movable in a horizontal plane operate to wrap the blank I5= around the mandrel, interlock the projections 18 and 19 to form a lap seam 20 and press the latter inwardly to fill the depression of the embossed part H. The result of this latter operation may be seen in Fig. 2 where it will be seen that the lock seam is inside the resulting sleeve thus leaving a substantially smooth outer surface.

Thus there is formed of thin strip metal a tubular sleeve for use as a shield in the basing of radio tubes and the like, such sleeve having a seam or look joint part way of its length with its outer face flush with that of the cylindrical wall, a sleeve held to a precise diameter with opposing end edges of portions above and below the seam in abutment with each other, or substantially so depending On whether the blank is slightly over or under length, so as to completely close the tube, such sleeve having a continuous annular flange along its top edge and an unobstructed bottom edge which permits the staking at any point of its periphery to an inner engaging surface.

As hereinabove stated, in the continuous high speed feeding of strip metal on a multiple slide machine slight variations in feed may result even though stops are set for gage-like accuracy. However, by an allowance for tolerance in dimen sion Y, Fig. 7, and by notching the strip and slitting it, as at stations A and B, respectively, a uniform product is rapidly produced in quantity and Without the wall of the shield at the ends of the seam being bulged by a crowding of its end edges or by a gap occurring by these edges being separated.

Attached to the inner surface of the shield there is shown at 2|, Fig. 6, a ground wire for connection with the lead wire in one of the terminals 5.

Although I have shown and described particular embodiments of my invention, I .do not desire to be limited to the embodiments de- 1. A base shield for plugin devices comprising a one-piece cylindrical sleeve formed from a unit length of strip metal, said strip unit being united at its ends by a lock seam extending but part way between its side edges, the opposing end edges of the strip portions at the ends of said seam abutting each other, the opposing end edges of said strip being slit a slight distance inwardly at each end of said seam whereby the outer face of said seam may be made to lie flush with the outer peripheral surface of the cylindrical wall and, said sleeve having an inwardly directed flange at one end.

2. A base shield for plug in devices comprising a one-piece cylindrical sleeve formed from a unit length of strip metal with an inturned annular flange at one end of the sleeve, said strip unit being united at its ends by a lock seam extending but part way between its side edges, the opposing end edges of the strip portions at the ends of said seam abutting each other, the opposing end edges of said strip being slit a slight distance inwardly at each end of said seam whereby the outer face of said seam lies flush with the outer peripheral surface of the cylindrical wall.

3. An electron tube including a glass envelope, a base of insulating material, an annular shoulder on said base concentric with said envelope, a cylindrical sleeve supported by said base and telescoping said shoulder for centering thereby in spaced relation to said envelope, said base having a plurality of regularly spaced radially extending slots, an undercut surface at the lower end of said slots and within the periphery of said shield, an inturned annular flange on the upper edge of said shield, means for holding said shield to said base comprising segmental portions pressed from the lower edge of said shield to engage said undercut surface, said shield being formed in one piece from strip metal joined at its ends by a lock seam of a length to leave marginal portions of the cylindrical body at each end of the seam, the ends of said marginal portions abutting each other in a line intermediate the sides of said seam, and a ring of basing cement providing a glass-to-metal seal between said envelope and said shield, the outer face of said seam lying flush with the outer peripheral surface of said sleeve.

CHARLES E. SCHELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 549,725 Johnson Nov. 12, 1895 697,622 Grifiin Apr. 15, 1902 1,475,399 Kronquest Nov. 27, 1923 1,513,636 Scholze Oct. 28, 1924 1,542,366 Brough June 16, 1925 1,560,692 Houskeeper Nov. 10, 1925 1,587,156 Houskeeper June 1, 1926 1,702,234 Goodridge Feb. 12, 1929 1,711,673 Crawford May 7, 1929 2,017,647 Betts Oct. 15, 1935 2,086,143 Van Hufiel July 6, 1937 2,093,199 Laxo Sept. 14, 1937 2,221,208 Sims Nov. 12, 1940 2,251,926 Erb Aug. 12, 1941 2,264,613 Borton Dec. 2, 1941 2,265,631

Coffin Dec. 9, 1941 

